1. Photosynthesis (PS)
Chapter 10

2. “Self” Feeders Autotrophs (producers)
Self-produce organic materials such as glucose using inorganic compounds like CO2 , H2O
Ultimate source of organic compounds for heterotrophs
Classes
Photoautotrophs
chemoautotrophs

3. Autotroph Classification
Photoautotrophs
use light as the energy source (photosynthesis)
in plants, algae, some protists, and some prokaryotes
Chemoautotrophs
- energy source from oxidizing inorganic substances (sulfur and ammonia)
unique to bacteria

4. “Other” Feeders Heterotrophs (Consumers)
Uses organic compounds created by others
1° Consumers (vegetarians)
2° Consumers (carnivores and omnivores)
Decomposers (detritivores)

5. Chloroplast Structure
Where within this organelle is the chlorophyll pigment located?
Chlorophyll pigment is embedded in the thylakoid membrane

6. Chloroplasts = Sites for PS
Found mainly in mesophyll cells (interior leaf tissue)
O2 exits and CO2 enters the leaf through stomata underneath the leaf.
Veins deliver water from the roots and carry off sugar from mesophyll cells to other plant areas.

7. PS Equation Net equation of photosynthesis:
6CO2 + 6H2O + light energy -> C6H12O6 + 6O2
In reality, photosynthesis adds one CO2 at a time:
CO2 + H2O + light energy -> CH2O + O2
(CH2O)n = generic formula for a sugar

8. 2 Stages of PS Light Reactions Requires Light Calvin Cycle
In Thylakoid Membrane
Requires Light
chlorophyll pigment absorbs light energy
Calvin Cycle
In Stroma
AKA Light Independent or Dark Reactions
** Be careful** occurs only during the day because NADPH and ATP made in the light reactions drive the Calvin Cycle

10. Absorption Spectra
In the thylakoid, several pigments differ in their absorption spectrum.
Chlorophyll a (dominant pigment) absorbs best in the red and blue wavelengths, and least in the green.
Other pigments (chll b, carotenoids) have different absorption spectra and
can transfer energy to chll a

11. Actions Spectrum
Collectively, these pigments determine an overall action spectrum for photosynthesis.

12. Photosystems Photosystem = light gathering complex
A few hundred chll a, chll b, and carotenoids combined = photosystem
Only chll a participates directly in the light reactions

13. Thylakoid Membrane Populated by Two Photosystems
P700 (Photosystem I) has a reaction center with an absorption peak at 700nm.
P 680 (Photosystem II) has a reaction center with a peak at 680nm.

14. Photosystem Function Sun E (photons) hit Photosystems
2 e- excited from chll a (stores PE)
Energy transferred from one pigment to another until E tranferred to chll a
Position of chll a is near the “reaction center” where 1st light driven chemical rxn of PS occurs

15. Light Reactions
Non-cyclic Electron Flow
Cyclic Electron Flow

16. Steps to Non-cyclic Electron Flow
1. P680 absorbs light
2. Light excites 2e- and passes e- to primary electron acceptor
3. Water is split into
½ O2  oxygen gas
H+  to thylakoid space
2e-  resupplies P680

17. Steps to Non-cyclic Electron Flow
e- pass through ETC, where they “fall” in E
E from e- is captured to produce ~ 1.5 ATP’s through chemiosmotic phosphorylation

18. Steps to Non-cyclic Electron Flow
e- from P680 replenish e- in P700
e- in P700 are excited again by light and passed to a primary electron acceptor

19. Steps to Non-cyclic Electron Flow
8. e- cascades down short ETC, where e- combine with and reduce NADP+ and H+ to form NADPH (E rich molecule)

20. Non-cyclic Electron Flow

21. Non-Cyclic Electron Flow
ATP and NADPH created in the Light Reactions are used in the Calvin Cycle

22. Cyclic Electron Flow
Calvin Cycle – uses up more ATP than NADPH so cyclic electron flow helps to generate more ATP’s
Short circuit – e- fall back from P700 primary electron acceptor to the 1st ETC to generate more ATP’s via chemiosmotic phosphorylation

23. Cyclic Electron Flow

24. Calvin Cycle (in stroma)
ATP drives the cycle
NADPH = reducing power for adding high energy e- to make sugar
3 Basic parts
1. CO2 fixation = Carboxylation
2. Reduction
3. Regeneration of CO2 acceptor (RuBP) – Ribulose bi-phosphate

25. CO2 Fixation
Rubisco catalyzes the fixation of CO2 to a C5 compound, RuBP (Ribulose biphosphate)
Initial C6 compound= unstable
Splits into PGA (3-phosphoglycerate)

26. Reduction Hydrolysis of 6 ATP NADPH is oxidized to NADP+
PGAL sugar created = G3P (glyceraldehyde-3-phosphate)
1/6 PGAL made into glucose and other organic compounds

27. Regeneration of RuBP
Hydrolysis of 3 ATP’s to regenerate RuBP

28. Evolution of Photorespiration
C3 plants = plants that make a C3 compound like PGA as the 1st product in the Calvin Cycle
In arid/dry climates, plants close stomata to prevent dehydration limits CO2 intake
Result  Rubisco accepts O2 in place of CO2
C5 intermediate results which splits into a C3 and C2 compound. C2 compound is exported as waste to peroxisomes and mitochondria to regenerate CO2 = photorespiration

29. Photorespiration – Detriment or not?
C2 waste and C3 compound created means no C5 RuBP regeneration for Calvin Cycle. This means reduced PS rate!!
no sugar made
C4 Photosynthesis and CAM Photosynthesis evolved to minimize photorespiration

30. C4 Photosynthesis Leaf Anatomy Differs b/t C3 and C4 plants
Bundle Sheath veins of leaf
Mesophyll outside of bundle sheaths loosely arranged
C4 plants = plants that have alternate CO2 fixation route that makes a C4 compound as the 1st compound (corn, grasses, sugar cane) C3

31. C4 Photosynthesis
CO2 fixed by PEP carboxylase (not Rubisco) in mesophyll cells
CO2 and combines with C3 PEP (phosphoenol pyruvate) to form OAA (oxaloacetate)
OAA converts to C4 malate
Malate enters bundle sheath cells via plasmodesmata
CO2 released from malate and captured by Rubisco to enter Calvin Cycle

32. CAM Photosynthesis CAM = Crassulacean Acid Metabolism
In succulent plants like cactus
Succulents open stomata at night and close them during the day, thus needing a way to fix CO2 at night

33. CAM Photosynthesis
At night, CO2 fixed by PEP carboxylase (not Rubisco)
Same chemical pathway as C4 PS to create malate except…
Malic Acid (malate) temporarily stored in Vacuoles at night
During the day, CO2 is released from the C4 malate and fixed by Rubisco to be used in the Calvin Cycle